JPH08321380A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE: To alleviate the photo-fatigue of an element material for extending the service life thereof, and allow full-color display by fitting a color filter to a transparent electrode used at least as one of electrodes clamping an organic thin film as a pair. CONSTITUTION: Regarding the organic EL element where an organic thin film 6 is clamped between electrodes 5 and 7 as a pair and at least one of the electrodes 5 and 7 is a transparent electrode, color filters 3 of red R, green G and blue B corresponding to the luminous color types of the film 6 are provided on the transparent electrode 5 as a light emission plane. As a result, external light of such wavelength as exciting each of three types of thin films 6 is absorbed with respective filters 3, and does not reach the films 6. Thus, each film 6 is protected against excitation due to the external light, and the photo-fatigue of the film 6 is alleviated. On the other hand, luminous light is allowed to pass the filters 3. Furthermore, the electrodes 5 and 7 are X-Y matrix type, and the color filters 3 are provided at the picture element section of the transparent electrode 5, so as to correspond to a luminous picture element, thereby ensuring full-color display. In this case, a black matrix 2 is preferably laid on the periphery of each picture element of the filters 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic thin film electroluminescent device (hereinafter referred to as an organic EL device) used for a flat light source or a flat display.
L element) and its manufacturing method. More specifically, it relates to an element that emits light by applying an electric field to a single-layer or multi-layer organic compound thin film.

[0002]

2. Description of the Related Art Organic EL devices have been small and lightweight since they have been capable of low voltage driving and have high brightness since they were published in Applied Physics Letters, Vol. 51, p. 913 (1987). Research aiming at application as a light emitting device has been actively conducted. The organic EL element has an organic compound as a light emitting substance, and can emit an image with a brightness of 1,000 Cd / m ² or more at a voltage of 10 V or less. Further, by selecting a light emitting substance, any light emission from blue to red can be obtained. It is characterized by possible all-solid-state devices. If the three primary colors are combined by making the best use of this characteristic, there is a possibility that it will be put to practical use as a small and lightweight full-color self-luminous display element that does not require a booster circuit. However, the biggest unsolved problem of this organic EL element is its short life and poor reliability. The cause of this short life is usually attributed to the oxidation of the electrode (cathode), the alteration of the material, the uniformity of the organic thin film, and the occurrence of film defects due to crystallization. However, other than the above factors, a major factor that accelerates the deterioration is light fatigue of the material forming the organic EL device, which has not been a problem until now. The principle of light emission of an organic EL element is to convert energy generated by recombination of holes and electrons injected through an electrode into light, and a material having such a function is known as a fluorescent substance. . Therefore, when irradiated with light having a specific wavelength determined by the material, the material is excited to emit fluorescence. When exposed to light for a long time,
The process of light excitation and light emission is repeated, so that light fatigue occurs in the material, its fluorescence intensity decreases with the passage of time, and finally it does not emit fluorescence.

Alkali glass is usually used as a support substrate for a transparent electrode constituting an organic EL element. The wavelength of the transmitted light differs depending on the type of glass, but it is roughly 3
It is 50 nm or more. Therefore, if the organic EL element is made of a substance having an absorption wavelength of 350 nm or less that efficiently excites molecules, the light that excites the molecules is absorbed by the glass and does not reach the material inside the element, so that unnecessary molecules are excited. Since it can suppress the light fatigue of the device, the life of the device is significantly improved. On the other hand, when an organic EL element is used as a display element or a lighting element, it must emit light in the visible range (approximately 400 to 700 nm). At this time, it is not necessary to emit all visible light,
Red (600 nm or more), Green (near 550 nm), Blue (4
By emitting light of the three primary colors (around 50 nm), full-color display is possible by adjusting light. Therefore, in the conventional configuration, if the light of the wavelength of 350 nm or less can be absorbed and the light of the above three primary colors can be obtained, the light fatigue of the organic EL element constituent material can be reduced, which is very effective. The energy difference between the light at the absorption wavelength and the light at the emission wavelength is the energy loss associated with the excitation-emission of the material. Most of this energy loss becomes heat, which is the main cause of raising the temperature of the device.
When the temperature of the element rises, crystallization of the organic EL element constituent material proceeds, which causes thermal destruction of the element. That is, the difference between the absorption wavelength and the emission wavelength of the material is preferably as small as possible. Therefore, a material that is excited by light having a wavelength of 350 nm or less for emitting red light causes large energy loss and is not practical. To prevent this, the wavelength to be cut should be lengthened.
It is proposed to install the UV cut filter disclosed in No. 95 on the front surface. However, as shown in FIG. 2, in the case of red light emission, the absorption wavelength is 500 nm, so a filter that absorbs light having a wavelength of 400 nm or less is not useful for improving light fatigue of a red light emitting material. Four
The filter will be colored by cutting the light of more than 00nm,
In addition to affecting the display color, the light emitted by the organic EL element is also absorbed, and the light is not emitted to the outside of the element, resulting in a decrease in element efficiency.

Since the organic phosphor has excited states having various energy levels and emits light according to the energy difference when the excited state transits to the steady state, its emission spectrum is generally broad. Cheap. The broad emission wavelength does not pose a problem in the case of a monochromatic light emitting element, but is not preferable in the case of aiming at a multicolor display, especially a full color display, because the tail of the emission spectrum deteriorates the color purity. As a means for avoiding this drawback, molecular crystal and liquid crystal, volume 227, p. 277 (1993) and JP-A-0.
It is recognized that the organic EL element disclosed in 6-325870 is used as a white light source and a color filter of three primary colors is installed on the front surface as in practical use in a liquid crystal display to display a color. There is. In the case of a liquid crystal display, the liquid crystal element is used simply for adjusting the light amount of white light, so that the white light source only needs to emit a certain amount of light. However, in the organic EL element, in order to display full color, it is necessary to change the amount of white light according to the display color. The amount of light is adjusted by adjusting the voltage applied to the pixel, but since the voltage-luminance characteristics of the phosphors that make up white light differ depending on the material, adjusting the applied voltage for dimming will produce a tint of the emitted color. Subtly changes. Therefore, it is unsuitable for a light source of a full-color display element in which a delicate color is a problem.
In addition, there is a drawback in that the time change of deterioration varies depending on the light emitting material, but even if an intended color can be obtained in the initial stage, a color shift occurs over time.

[0005]

By providing a color filter corresponding to the emission color of each pixel arranged in a matrix of the organic EL element on the light emitting surface side, light fatigue of the organic EL element material is alleviated. The present invention has been completed on the basis of this finding that it has been made possible to obtain a luminescent color having a desired color purity with a long life. As is apparent from the above description, it is an object of the present invention to solve the above-mentioned problems and provide a self-luminous flat display that has a long life and is capable of full-color display.

[0006]

The present invention has the following constitution. (1) An organic EL element having an organic thin film sandwiched between a pair of electrodes, at least one of which is transparent, wherein a color filter is installed on the transparent electrode side. (2) In an organic thin film EL element in which an organic thin film is sandwiched between a pair of XY matrix electrodes, at least one of which is transparent, a color filter is installed in a pixel portion on the transparent electrode side. (3) Organic E, characterized in that the color filter according to the item (1) or (2) is red, green and blue
L element. (4) An organic EL device characterized in that the color filters according to item (1) or (2) are red and green. (5) An organic EL device characterized in that a black matrix is arranged in the peripheral portion of each pixel of the color filter of the item (1) or (2).

[0007]

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows the relationship between the relative transmittance of a color filter and the wavelength. R is an example of a red filter, G is a green filter, and B is an example of a blue filter. Red filter is 60
Light having a wavelength of 0 nm or more is transmitted, but light having a wavelength of less than that is not transmitted. The green filter transmits light near 500 nm, but does not transmit light below 400 nm and above 600 nm. The blue filter transmits light near 450 nm, but does not transmit light below 350 nm and above 550 nm. FIG. 2 shows an example of the case of red light emission, which is the measurement result of the fluorescence intensity of DCM having the structure shown in [Chemical Formula 1].

[0008]

Embedded image

The peak of the excitation light is around 480 nm,
This excitation light is absorbed and light near 600 nm is emitted. Combining with the result of the red filter R shown in FIG. 1,
Since the filter absorbs external light having a wavelength near 480 nm, which is the absorption wavelength, and the light does not reach the DCM, excitation by external light can be prevented and the cause of optical fatigue can be removed. Moreover, since light of 600 nm or more is transmitted, DC
Since the red light from M is transmitted, it becomes a red light emitting element. Similarly, FIG. 2 shows an example of Alq shown in [Chemical Formula 2] in the case of green.
It is a measurement result of the fluorescence intensity of.

[0010]

Embedded image

As in the case of the red color, the color filter absorbs the light that excites Alq and transmits the light that emits light, so that it can be used as a green light emitting element.

[0012]

Embedded image

OMS represented by [Chemical Formula 3] as an example of blue color
It shows the measurement result of B. It functions in exactly the same way as the former two and can emit blue light. If color filters are installed according to the light emitting pixels in this way, excess external light can be absorbed and the light excitation of the light emitting material can be suppressed, and the light from the light emitting material can be transmitted and emitted to the outside. From the above, it is possible to obtain the emission colors of the three primary colors required for full-color display. Further, since unnecessary excitation of the fluorescent substance is suppressed, its effect can be known by a light exposure test as shown in the examples.

As can be seen from FIGS. 2 to 4, the emission color of the organic compound has a trailing edge, so that there is a problem in color purity when a full color is to be exhibited. By using a color filter together as in the present invention, it is possible to obtain a display having an image quality equivalent to that of a liquid crystal display currently in practical use.

An embodiment of the present invention is schematically shown in FIG. A black matrix (2) having a predetermined pattern is arranged on a transparent substrate (1) such as a glass substrate. This black matrix is installed so that adjacent colors do not become identical to each other (to improve color purity), and may be anything as long as patterning is easy and light can be shielded. Usually, a black pigment type color filter or a chromium film (preferably a low reflection chromium film) is used. The black matrix is installed to improve color purity and is not an essential requirement. A red (R), green (G) and blue (B) color filter (3) is formed thereon.

The color filter is, for example, a technique for producing a color filter for a liquid crystal panel (Tricheps Co., Ltd., 19).
1991). Illustrative examples include a pigment type in which a pigment is dispersed in a photocurable resin, a dyeing type in which a pigment is colored by dyeing, or an electrodeposition method.
The blue color filter does not necessarily have to be installed when an ultraviolet cut filter is installed inside or outside the transparent substrate to prevent discoloration.

Next, an overcoat film is applied to eliminate the step. Acrylic-based, epoxy-based, or imide-based resins are usually used for the overcoat film. An ITO thin film which is a transparent electrode is formed thereon by vapor deposition, sputtering, or another method, and is patterned by photolithography to form a predetermined stripe pattern. A light emitting layer that emits a color corresponding to the color filter is laminated thereon. This light-emitting layer is a laminated type described in Journal of Television Society, Vol. 44, p. 578 (1990), and JP-A-04-212286 and Japanese Patent Application No. 06-79.
914 and the like.

Here, the layered type is a layered type in which materials constituting an organic EL element are classified according to their functions, and a hole injecting and transporting material, a light emitting material, and an electron injecting and transporting material are laminated, and holes are injected and transported and light is emitted. Or a compound having an electron injecting and transporting ability and a light emitting ability to form a two-layer structure. Further, it goes without saying that the hole transport layer and the electron transport layer may be formed as a plurality of layers to improve the efficiency. The mixed type refers to a layer in which a hole injecting / transporting material, a light emitting material, and an electron injecting / transporting material are mixed to form a single layer.

As a method of patterning the three primary colors at desired positions, Japanese Patent Laid-Open No. 03-269995 and Japanese Patent Laid-Open No. 06-
A method such as that described in 13184 or Japanese Patent Laid-Open No. 05-258859 may be used, and any method or means may be used. Then, a metal or a metal mixture having a low work function is formed into a cathode by a method such as vapor deposition. A factor that adversely affects the life is removed by, for example, putting the device thus produced in a protective case or coating it with a resin.

[0020]

【Example】

Example 1 As a light emitting material, 1 part by weight of DCM represented by [Chemical Formula 1] and 1 part by weight of polycarbonate were added to 1,2-dichloroethane 100.
After dissolving in parts by weight, by a spinner according to a conventional method,
It was applied onto a washed glass substrate and dried at 80 ° C. for 1 hour.
Under a fluorescent lamp in a room, a red filter that transmits a wavelength of 600 nm or more was installed and light irradiation was performed. The change in emission intensity after 100 minutes was small.

Example 2 A thin film was applied and dried on a glass substrate in the same manner as in Example 1 except that Alq represented by [Chemical Formula 2] was used as a light emitting material, and the peak wavelength of transmitted light was 535 nm. A certain color filter was installed, and the change with time of the emission intensity was measured, but it hardly changed even after 100 minutes.

Example 3 A thin film was coated on a glass substrate in the same manner as in Example 1 except that OMSB represented by [Chemical Formula 3] was used as a light emitting material.
After drying, a color filter having a peak wavelength of transmitted light of 460 nm was installed and the same measurement was performed, but the change was small.

Comparative Examples 1 to 3 The organic thin films prepared in Examples 1 to 3 were directly exposed to a fluorescent lamp without passing through a color filter. After 100 minutes, the emission intensity changed significantly. These results are summarized in FIG. You can see that the effect of the color filter is clear.

Example 4 An example in the case of a matrix type device will be described below. Organic E
The production of the L element portion was based on Japanese Patent Laid-Open No. 06-79914. FIG. 7 shows a schematic diagram thereof. The glass substrate (1) that has been thoroughly washed is set in a vacuum vapor deposition tank, a shadow mask is placed between the glass substrate and the vapor deposition source, and chromium vapor deposition is performed to form a striped black matrix (2). The glass substrate on which chromium is vapor-deposited is taken out from the vapor deposition tank, and CR-2000 manufactured by Fuji Hunt Electronics Technology Co., Ltd. is applied by spinner in order to install a red filter. Prebaking is performed in a nitrogen atmosphere, and exposure is performed in a nitrogen stream. Next, after development and washing with water, post-baking is performed. In this way, the red filter (3
(R)) is completed. To obtain a green filter (3 (G)), CG-2000 is spinner coated and the same operation is repeated. Spinner coat the last CB-2000 to make a blue filter (3 (B)).
Complete the primary color filter. Overcoat layer (4)
Optomer S manufactured by Japan Synthetic Rubber Co., Ltd.
S-1211 is spinner coated and then baked.
This substrate is placed in a vacuum chamber and an ITO transparent electrode is attached.
The substrate is taken out from the vacuum chamber, and a striped transparent electrode (5) is formed by a photolithography method according to a conventional method. 2 different height by photolithography method
Seed columns (10 (a), 10 (b)) are placed along the transparent electrode. This substrate is brought into a vacuum chamber, and copper phthalocyanine is first vapor-deposited from the direction a as a hole injecting and transporting material to form a thin film (11) on the entire surface. Then, the OMSB used in Example 3 is vapor-deposited from the direction b to form a thin film (12). Alq used in Example 2 was vapor-deposited from the direction c, and the green light emitting layer (13) was used, followed by DC used in Example 1.
The red light emitting layer (14) is formed by evaporating M from the direction a.
By performing the above operations, the EL with three primary colors
A light emitting layer was formed. Finally magnesium from direction d /
Co-deposited silver was used as a cathode. Organic E created in this way
The L element was placed in a nitrogen stream and a voltage of 10 V was applied.
Even after 100 hours, a beautiful light emission was shown.

Comparative Example 4 Except for Example 4 and the process of making a color filter,
A similar organic EL device was created, and the same 10
When a voltage of V was applied, light emission was uneven in 3 hours.

[0026]

As described above, the organic thin film E of the present invention is
The L element is extremely useful as a flat light source or a light emitting element for a display.
The device can have a long life, and full-color display is possible, and its industrial value is high.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the transmittance and wavelength of color filters of three primary colors.

FIG. 2 is an excitation and emission spectrum of [Chemical Formula 1].

FIG. 3 is an excitation and emission spectrum of [Chemical Formula 2].

FIG. 4 is an excitation and emission spectrum of [Chemical Formula 3].

FIG. 5 is a schematic view of an organic EL element.

FIG. 6 is a comparison of changes over time in fluorescence intensity with and without a color filter installed.

FIG. 7 is a cross-sectional view of an organic EL device of Example 4.

[Explanation of symbols]

 1 Glass Substrate 2 Black Matrix 3 Color Filter 4 Overcoat Film 5 Transparent Electrode (Anode) 6 Light Emitting Layer 7 Metal Electrode (Cathode) 8 Protective Resin 9 Ultraviolet Cut Filter 10 Support 11 Hole Injection Transport Layer 12 Light Emitting Layer (B) 13 Light emitting layer (G) 14 Light emitting layer (R)

Claims (5)

[Claims] 1. An organic electroluminescence device having an organic thin film sandwiched between a pair of electrodes, at least one of which is transparent, wherein a color filter is installed on the transparent electrode side. 2. An organic thin film electroluminescent device in which an organic thin film is sandwiched between a pair of XY matrix-type electrodes, at least one of which is transparent, wherein a color filter is installed in a pixel portion on the transparent electrode side. Electroluminescent device. 3. An organic electroluminescent device, wherein the color filter according to claim 1 or 2 is red, green or blue. 4. An organic thin film electroluminescent device, characterized in that the color filters according to claim 1 or 2 are red and green. 5. An organic electroluminescent device comprising a color filter according to claim 1 or 2 in which a black matrix is arranged in the peripheral portion of each pixel.